1 Simulations of signal and background for an Nnbar Experiment with Free Neutrons A. R. Young, D. G. Phillips II, and R. W. Pattie, Jr. North Carolina State University Triangle Universities Nuclear Laboratory on behalf of the NNBarX Collaboration 2 Overview Detector Strategy Review and General Detector Specifications Antineutron Annhilation Events A Proto-Detector for Neutron-Antineutron Oscillations MC Acceptance Results Background Analysis and Challenges 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop 3 ILL Layout 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Free neutron n-nbar search experiment in at ILL [1]: measured P NNBar < x sensitivity: N n t 2 = 1.5 x 10 9 s 2 /s (90% CL) 4 ILL Detector Configuration 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop E thresh > ~800 MeV, at least 1 charged particle track, at least 2 tracks which reconstruct as emerging from target Effective run time = 2.4x10 7 s, N events = 6.8x10 7 n-nbar detection efficiency (/4 = 0.94): 52% 2% No background & no candidate events after analysis. 5 m 5 ILL Detector Configuration Cosmic-Ray Veto ILL Cosmic-Ray Veto (CRV) 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop ILL Calorimeter: 12 LST planes interleaved w/Pb & Al plates. ILL Vertex Detector [6]: ILL Scintillator Counters [4,5]: ILL Target [2,3]: 130 m thick. 10 LST planes operated at 4.6 kV Vertex = 4 cm; 6.0x10 4 electronics chnls. 6 ILL Experiment: Backgrounds 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Backgrounds which scale with source strength or CN current s & fast ns from reactor: s from n capture in propagation region and target (not shieldable contribution due to abs. on target of incident beam) Eliminated w/ bent 58 Ni guides in shielding crypt before propagation region Capture on beamline surfaces: Complete containment of n-beam in propagation region (2% losses) 8 rings of 10 B-enr. glass in drift vessel (absorb vertically falling ns), 6 LiF beam dump Residual beamline and target capturesstochastic background Drives trigger criterion: 400 MeV threshold, one charged track, two total tracks (timing signal) 7 ILL Experiment: Backgrounds 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Backgrounds which are independent of source or CN-beam time structure: cosmic-rays activation Veto layer Timing layers (veto inward-going) Trigger and track reconstruction: must reconstruct to target and have at least one other calorimeter track 8 NNBar at ESS 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Adapt detector to pulsed cold neutron source driven by 5 MW spallation target with very large increase in flux due to concentrating optics Goal: 0 background events, >.5 for annihilation events Background Challenges: High energy n/p backgrounds present during proton beam Larger CN fluxes and optics will increase capture gamma rates Fast ns (0-10 MeV) present due to beta-delayed ns Larger detector volume will increase cosmic and capture gamma rates Must be sufficient for longer running periods (1y for ILL3y+) 9 Overall Simulation Strategy First Steps 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Scale successful ILL geometry to larger beam and target size required for next generation experiment Develop generalized geometry with modern degree of granularity using GEANT framework (perhaps overkill here to begin with) Evaluate state-of-the art for the annihilation vertex (exploring impact of GENIE-based simulation of decay modes and pion-fields interaction in nucleus) Implement geometry-specific analysis of backgrounds (begun with NNbarX experiment) using appropriate analysis tools, typically MCNP-X/MCNP-6 in addition to GEANT4 10 NNBar Proto-Detector Simulation: a Work in Progress -All sims use Geant (with every known library installed). -GENIE nnbar event generator (5e4 events available). -In this preliminary study, randomly selected 5e3 nnbar events. -Generated 5e4 background events (n & p singles). -Detector geometry consists of target, straw tube tracker & Minerva-style polystyrene/Pb calorimeter. -Target is 100 um, 2 m diameter 12 C disk. Vacuum tube is 2 cm thick Al. 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Geant simulations by D. G. Phillips, II 11 NNBarX Annih. Event Simulation 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Branching Fractions X-sections rescaled for 12 C Annihilation Point Inv. mass of mesons leaving nucleus SK ( 16 O) NNBAR r (fermi) GeV Annih. event generator based on IMB expt. code (K. Ganezer, B. Hartfiel, CSUDH) Baseline: 12 GENIE: NNBar Final State Primaries A. R. Young, D. G. Phillips II, R. W. Pattie Jr.6/13/14 Final State Pionic ModeNevents% Total + - 2 % 2+-02+- % +-0+- % 2 + - 2 % + - 3 % 2 + 2 - % + 2 % + 3 % +-+- % +0+ % + 2 - % 2 + 2 % GENIE-2.0.0: intranculear propagation based on INTRANUKE C.Andreopoulos et al., The GENIE Neutrino Monte Carlo Generator, Nucl.Instrum.Meth.A614:87-104,2010. Final state list prepared by R. W. Pattie Preliminary 13 NNBar Proto-Detector Simulation /13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Annihilation Mode Event n + 12 C -> 11 C + 3 0 ( 45, 268, 320 MeV ) + + ( 81 MeV ) + - ( 207 MeV ) +-+- Legend 14 6/13/14 NNBar Proto-Calorimeter Geometry MINERvA images credit: E. Ramberg (FNAL) Calorimeter 20 layers of 4 cm thick Scint +0.2 cm thick Pb. MINERvA-style Extruded Scintillator A. R. Young, D. G. Phillips II, R. W. Pattie Jr. 15 6/13/14 ATLAS TRT Assembly at Indiana University NNBar Proto-Tracker Geometry Tracker 5 mm kapton straws Fill gas: 70% Ar, 30% CO 2. 50XY planes (0.5 m thick). = g/cm 3 A. R. Young, D. G. Phillips II, R. W. Pattie Jr. (4 cm diam in fig.) 1.3 e6 straws 16 Event Reconstruction 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. 6/13/ n + 12 C -> 11 C + 3 0 + - 17 NNBar Final State Primaries (Signal) A. R. Young, D. G. Phillips II, R. W. Pattie Jr.6/13/14 18 Energy Threshold Acceptance (Signal) ILL Trig. Thresh. 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. 19 Tower Hit Acceptance (Signal) ~ILL 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. 20 Timing Window Acceptance (Signal) ILL 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. 21 MC Acceptance Summary 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Cut DescriptionSignal Acc.Bkgd Acc. Cut 1: E cal < 400 MeV98.50%0.22% Cut 2: Cut 1 + (NTrkrTowerHits & NCal TowerHits) > %0.00% Cut 3: Cut 2 + E cal < 500 MeV w/in 50 ns91.74%0.00% Conclusion: the proto-detector could in principle provide improved detection efficiency relative to the ILL experiment for n-nbar events using modern technology Challenges: how to minimize cost and meet background rejection goals 22 Missing Events 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Final State Pionic ModeNMissEvnts % Total +-0+- % +-+ % 2+-02+- % + 2 % 2 + 2 - % 2 + 2 % + - 2 % 2+-2+ % + 2 - % + 2 % 2 % - 2 % 23 Background Simulations: A Prospectus 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Simulation which addresses problem of a false positive is challenging: must suppress rate after cuts to < Hz! ILL experiment provides a baseline from which we can scale ESS: CN flux on target 100 CN lost in transit 3000 also new potential sources of bkg Specific challenge: beam-generated backgrounds very closely tied to geometry of source, CN beam and shielding geometry! 24 Reminder: unique capability to test for false positive with free neutron expt! 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Oscillation phenomenon switched off when magnetic field at mG level (backgrounds not affected)! Dedicated runs possible with free neutron expt to explore false positive: Second graphite target placed after first to explore event reconstruction to second target (all annihilation products removed from beam) G. Greene 25 Sources of Background 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Stochastic gamma backgrounds Capture in beam-tube (distributed,shieldable) ~10 12 /s Capture on target (not shieldable) ~10 10 /s CN scatter from target into detector High energy n,p (~20 n/p at source) Beta-delayed n Cosmic rays Not important for ILL experiment 26 Gamma Backgrounds 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Design experiment so gamma backgrounds dominated by capture on 10 B (beam baffles) or 12 C (target) highly geometry dependent! Simulation task: 1.Assess passive (shielding) strategy to reduce beamline backgrounds 2.Assess active detector event reconstruction for improved suppression factors 27 Beamline Gamma Backgrounds 10 B beam baffles preferred because no fast n branch and resultant gamma ( 10 B + n 7 Li + + (0.48 MeV), 94% of time) possible to shield (increase number from 8 used on ILL expt) Explore recessed detector geometry to further limit fluxes from beamline (may be necessary for ESS experiment) no line of sight to beam-dump, limited line of sight from near beamline baffles 1.Currently using MCNP-X/MCNP6 for beamline shielding studies 2.Must integrate with Geant4 detector simulations detector 6 LiF beam dump shielding 10 B glass rings Stepped Tube Background Intensity Simulation Performed for 1e5 neutrons crossing Target Plane, 1b Deuterium Moderator Source. Large section of tube is 4 meter radius. Normalized to source statistics,source intensity, and bin size (0.6 meters) Note the Step at 190 m has a ~100x higher interaction 10% Statistics or better in each bin. Matthew Frost: UTK Tapered Tube Background Intensity Simulation Performed for 1e5 neutrons crossing Target Plane, 1b Deuterium ESS Moderator. Large section is 4 meter radius and tapers to 2 meters over 30 meters along beam. Normalized to source statistics,source intensity, and bin size (0.6 meters) Intensity is identical after target position (200 meters) as in the stepped geometry. Taper begins at 170 m 10% Statistics or better in each bin. 30 Target Gammas 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Ensure contaminants (H, N) at adequately low levels H < 0.1% Relatively straightforward event generator for 12 C (dominated by emission of one 4.95 MeV gamma) see next slide Simulation task: evaluate suppression based on absence of pion-like tracks which point to target Tied closely to trigger logic Signal proportional to time window factor of 5 improvement possible w/ modern dets (still need at least factor of 20) Particle-ID in calorimeter and position resolution for pointing-to- target are good candidates for making up needed suppression (how to implement tracklike cuts at trigger level perhaps duplicate previous cut using factor of 100 more detector subvolumes, and perhaps an adjacent volume summing ) Interesting problem on to-do list! 31 Prepared by B. M. Vorndick (Essentially 100% prob. for ~5 MeV in gammas) Target Event Generator Capture gammas from n+ 12 C and n+ 10 Be May be advantages to Be target (thanks to P. Bently) 32 High Energy n,p Backgrounds 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Serious consideration for experiments at a CW spallation source 5 s cut around primary proton beam pulse adequate to complete suppress H.E. primaries at ESS! (CN mean transit time a few ms, ESS pbeam pulse every 71 ms) ESS Shielding strategy important: P. Bentleys talk High energy products from 1 GeV proton beam incident on W target (at 90 degrees) MARS calculation by S. Striganov (Performed studies of CW fast n backgrounds using MCNP) 33 Input for Simulations: High Energy n Detection Efficiency 6/13/14A. R. Young, D. G. Phillips II, R. W. Pattie Jr. First attempts to model high energy neutron detection efficiency for gas detectors with Geant4 problematic (note: part of both nnbar signal and backgrounds) Collaboration has undertaken a campaign to assess absolute detection efficiency for plastic scintillator and gas detectors at WNR facility 34 WNR Tests - Layout 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop LANL WNR-15R Beamline 250 MHz 8-chnl 12-bit fADC Predicted n-flux 20m from target 35 WNR Tests - Fission Foil 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Fission Chamber TOF Spectra Blue = MCNPX Red/Black = Fission Foil Data (Agreement good) Efficiency results 36 37 Agreement with Monte Carlo (Geant Libraries): current status 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop 1. Generic Hadron No neutron scattering 2. HPLE+IBC - This uses the High precision Low Energy libraries for E_n